Tests of general relativity on cosmological scales are essential to distinguish GR from other alternative gravity models. One way to achieve this is by probing the growth of structure down to percent-level, but this is challenging. I will show it may be achievable if we combine a photo-z survey with a spec-z survey over the same (large) area of the sky. The error budget on the growth parameter can be effectively reduced by combining redshift space distortion with weak gravitational lensing over the same survey volume. Alternatively, I will show that voids present in large-scale structure may be sensitive probes to certain types of modify gravity. I will also go through some challenges in applying these probes.